1. Field of the Invention
The present invention relates to a belt driving device in which an endless belt spans around a drive pulley and a driven pulley and the belt is driven by rotation of the drive pulley, and more particularly to a belt driving device including a belt shift correcting member for correcting shifting of the belt.
2. Discussion of the Background
A belt driving device in which an endless belt spans around a drive pulley and a driven pulley so as to be driven by rotation of the drive pulley is known to be configured as a sheet conveying device or a photoconductor belt unit for an image forming apparatus such as copying machines, printers and facsimiles. Such a belt driving device is also known to be configured as a device for conveying various products or a device for transmitting power.
In such a belt drive device, if the belt shifts in a width-wise direction while being driven, products being conveyed by the belt can not be properly conveyed. Therefore, the belt driving device generally has a device to correct shifting of the belt.
For example, a belt driving device is known in which a flange is provided at axial ends of a pulley around which an endless belt is spanned for regulating shifting of the belt in its width-wise direction. However, in such a device, when the width of the belt is wide, for example, as in a sheet conveying device for an image forming apparatus, the belt is shifted by a relatively strong force and thereby an end of the belt is abutted against the flange with a strong pressure which results in damage to the end of the belt.
Also, it is known that a pulley around which a belt is placed is formed in a drum-like shape for preventing the belt from shifting. Further, a belt shift correcting device is known in which shifting is corrected by utilizing behavior of a part of a belt protruding over an axial end edge of a pulley around which the belt is wound. However, these devices have a deficiency in that shifting of a relatively wide belt can not be effectively corrected.
Additionally, a method of correcting shifting of a wide belt is known in which shifting of the belt is detected by a detecting device and the degree from horizontal of a pulley around which the belt is wound is adjusted in accordance with a result of detecting shifting of the belt. However, the structure of a device incorporating this method is complicated and the cost is high.